This application provides a command line tool for documenting hardware and software designs through ideal timing diagrams. It reads signal descriptions from a text file with an intuitive syntax, and outputs an ideal timing diagram to an image file. Notation typical of timing diagrams found in the Electrical Engineering discipline is used, including arrows indicating causal relationships between signal transitions.

The options are as follows:

−-help

Show usage reminder.

−-verbose

Increase diagnostic output.

−-scalefactor

Scale the diagram by the given factor. The default scaling factor is 1.0.

−-pagesizeWidthxHeight

Scale the diagram to fit given image size.

−-aspect

Maintain fixed aspect ratio if --pagesize given.

−-cell-heightH

Height of the each signal in pixels. Default is 32.

−-cell-widthW

Width for the time unit in pixels. Defaults is 64.

−-font-sizepts

Font size in pts. Default is 18.

−-line-widthW

Line width for drawings in pixels. Default is 1.

−-outputtarget

The name and format of the output image is determined by target.

file ...

The input files describe the signals to be diagrammed. See the FILES and EXAMPLES sections for a description of their format.

FILES

The following is a technical description of the input file syntax and semantics. If you are reading this for the first time, you may want to skip ahead to the EXAMPLES section.

The input file consists of a series of statements describing the signal transitions during each clock period of the timing diagram. Whitespace and comments following a ‘#’ are ignored.

SIGNAL=VALUE

This statement changes the value of a signal at the beginning of the current clock, and adds it to the list of signal dependencies. The signal name may consist of one or more words consisting of alphanumerics and underscores joined by periods, ‘signal.name’, for example. The signal value format is described further on.

SIGNAL

This statement adds a signal to the list of dependencies without changing its value.

Statements are seperated by the following symbols:

,

The comma seperator is used to seperate statements without affecting the dependency list or clock (ie: the next statement will add to the dependency list).

;

The semicolon seperator resets the list of dependencies without incrementing the clock

.

The period seperator resets the list of dependencies and increments the clock.

=>

The "causes" seperator renders dependency arrows based on the current list of dependencies and then resets the dependency list.

-tD>

The "delay" seperator renders a delay arrow from the last dependency with the annotation tD.

Signal values are rendered according to the following rules:

0, 1, true, false

A binary high/low signal.

tick

A clock pulse which repeats.

pulse

A one-shot clock pulse.

X

A don’t care value.

Z

A tristate value.

"ABC"

Any other alphanumeric token, or text enclosed in quotes is rendered as a state. For example, ‘"1"’, is rendered as a state, whereas, ‘1’, is rendered as a high signal.

This input file descibes the changes in five signals over a period of seven clock cycles. The end of each clock cycle is indicated with a period. For example, the following line indicates a single signal, named ‘FIRE’ became true during a clock cycle:

FIRE=1.

The first clock period of the input file provides the initial value for all signals to be diagrammed. The signals will appear on the timing diagram in the order they first appear in the input file. Signals are assumed to have the "don’t care" value if their initial value is not given.

Independent signal transitions which occur simultaneously are normally seperated by commas. Since signals aren’t normally expected to change simultaneously, the initial state is a good example of this:

POWER=0, FIRE=0, ARMED=0, LED=OFF, COUNT=N.

Dependencies can also be indicated for a signal transition. Dependencies are rendered as arrows on the timing diagram from the last change in each dependency to the dependent signal transition. Here, the previous change in the state of ‘FIRE’ causes a change in the ‘ARMED’ signal.

FIRE => ARMED=1.

To indicate that a change in one signal causes an immediate change in another signal, list both signal changes in the same clock period:

POWER=1 => LED=GREEN.

For signal state changes with multiple dependencies, seperate the dependencies with commas:

FIRE, ARMED => LED=RED.

Sometimes, a single dependency causes multiple independent signals to change. Use a semicolon to start a new list of dependencies. Modifying the previous line to indicate that ‘FIRE’ also causes ‘COUNT’ to increment yields:

FIRE, ARMED => LED=RED;
FIRE => COUNT="N+1".

You can find this example and others along with their generated timing diagrams on the homepage for drawtiming at ‘http://drawtiming.sourceforge.net’.